Fiber-based carrier structure for liquids and solid particles and method for producing the fiber-based carrier structure

ABSTRACT

A fiber-based carrier structure is made of fractions of industrially produced reinforcing fibrous materials, which contains endless fibers in a tangled arrangement as a first reinforcing fiber component and which contains endless fiber bundles as a second reinforcing fiber component. The fiber-based carrier structure further has a pore system. Accordingly, the endless individual fibers and the endless fiber bundles are used as a mixture preferably in an isotropic tangled arrangement to produce a fiber-based carrier structure, the pore system of which is an open-cell pore system and is openly accessible from outside. The fiber-based carrier structure enables the absorption of liquids and/or solid particles by the selection of a defined mixture ratio of endless fiber bundles and endless individual fibers. A capacity to be impregnated with and the capacity to absorb liquid and/or solid powdery materials can be set by the mixture ratio.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation application, under 35 U.S.C. §120, of copendinginternational application No. PCT/EP2014/053201, filed Feb. 19, 2014,which designated the United States; this application also claims thepriority, under 35 U.S.C. §119, of German patent application No. DE 102013 002 861.2, filed Feb. 20, 2013; the prior applications are herewithincorporated by reference in their entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a fiber-based carrier structurecontaining proportions of industrially produced reinforcing fibermaterials, containing finite fibers in a random arrangement as a firstreinforcing fiber component and containing finite fiber bundles as asecond reinforcing fiber component, wherein the fiber-based carrierstructure further has a pore system.

International patent disclosure WO 2012/072 405 A1, corresponding toU.S. Pat. No. 8,840,988, describes a fiber preform having unidirectionalslivers which is composed of two zones which are different from oneanother. This known fiber preform thus has an anisotropic structure. Ina first zone there are arranged reinforcing fiber bundles which have aresin composition, while the second zone contains a unidirectionallyoriented reinforcing yarn strand and likewise a resin composition. Thepurpose of this document is to provide a fiber preform which makes itpossible to adapt to local stresses in the component.

International patent disclosure WO 2010/139077 A1 describes a method forproducing a composite material having the features of the generic typementioned at the outset. It contains a core layer that contains at least20 vol. % air voids and is made of a thermoplastic reinforced withrandomly oriented fibers, and reinforcement strips made of continuous,parallel, unidirectional reinforcement fibers, which are embossed intothe surface of the core layer on one side or on both sides. Thereinforcement fibers of the outer layer are thermally fused onto thecore layer by thermoplastic binders. It is not clear how the air voidcontent in the core layer could purposively be adjusted, or whether thevoids are accessible from the outside at all. There is high productanisotropy between the core and the outer layer. The reinforcement fiberstrips embossed into the surface of the core layer are oriented so as tobe parallel to one another. This document relates to producing acomposite material having high strength and stiffness, which has goodsound absorption. The voids have no significance for the absorption ofliquids or solid particles, that is to say impregnability is not sought.

Published, non-prosecuted German patent application DE 10 2007 012 608A1, corresponding to U.S. Pat. No. 8,568,549, relates to a method forproducing a preform for a fiber composite structure that is inaccordance with the force flux, in which a flat fiber band obtained byspreading a fiber bundle is placed at a predefined position and thenfixed by a binder material. Because in this case it is desired toarrange the fiber bands in accordance with the load, high productanisotropy is obtained. No defined mixtures of single fibers and fiberbundles are used.

Published, non-prosecuted German patent application DE 10 2008 026 161A1 describes a method for producing a fiber composite component, inwhich there are used continuous reinforcing fibers which are combinedwith a matrix material in the immediate vicinity of a shaping nozzle toform an impregnated fiber material. This document also relates toarranging reinforcing fibers in accordance with the load, which leads tohigh anisotropy in terms of fiber orientation, continuous reinforcingfibers being used.

In the production of fiber layers in the conventional textile industryin the field of nonwovens or nonwoven-like fillers, the aim is always100% complete separation, where possible, of the finite fiber materialsthat are used. Any residual fiber bundles that are still present, whichare also referred to as cut bundles in the case of chemical fibers, aredefined as defects and, where possible, should not occur. Consequently,according to the current prior art, nonwovens are referred to which arecharacterized in that they consist of fibers whose position can bedescribed only by methods of statistics. Nonwovens are distinguished bythe fiber material (for example the polymer in the case of chemicalfibers), the bonding method, the type of fiber (staple or continuousfibers), the fineness of the fibers and the orientation of the fibers.The fibers can thereby be laid specifically in a preferential directionor can be oriented entirely at random, as in the case of a random-layernonwoven or random nonwoven. A nonwoven having defined proportions offiber bundles and single fibers as a carrier structure for substancesand the use thereof in the field of fiber composites is hithertounknown. The carrier structure can here range from a loose fiber fillingto the consolidated 2D and 3D structure, for example nonwoven=2D.

Conventional nonwovens, which can be bonded mechanically, thermally orchemically, have, depending on the fiber material, fiber geometry(thickness, length), fiber material mixture and production orconsolidation, demonstrable properties for binding liquids or solidparticles in the form of powders. In the case of liquids, a specificabsorption capacity is referred to, which manifests itself in theabsorption of more or less large amounts of liquids—which in most casesare aqueous, low-viscosity systems for applications in the field ofcleaning or soaking up within the meaning of disposal—in a nonwoven intothe inner layers thereof. Viscous liquids or melts can only be absorbedat the surface of the nonwoven without additional measures. As theviscosity of the liquid increases, it becomes increasingly difficult totransport it into the core of a nonwoven layer. Assistance is providedhere by long impregnation times, with additional complex suctioning ofthe nonwoven, for example by vacuum or by pressure injection, with onlylimited success.

It is similarly problematical to introduce solid particles in the formof powders or fine particles into such conventional nonwovens of singlefibers. In most cases they remain on the surface of the nonwoven andpenetrate only into layers that are close to the surface. Thenarrow-pore system of voids when single fibers are used prevents deeperpenetration into the core of the nonwoven. This high capacity ofconventional nonwovens to retain particles is used to advantage forexample in dust or aerosol filtration but is extremely obstructive inother fields of application, for example in the production offiber-reinforced plastics materials, where subsequently curing matrixmaterials in the form of viscous liquids or powders must be introducedas homogeneously as possible into reinforcing fiber nonwovens, loosefillings or mats.

In the field of fiber-reinforced plastics materials, pulverulent bindersubstances and highly viscous liquid binders must uniformly penetratereinforcing fiber layers that are as thick as possible in order toobtain an uniform fiber content over the product cross section in thesubsequent fiber composite material. Assistance is provided in this caseby the occasional use of mats of 100% cut fiber bundles. Although suchwhat are known as cut roving mats, for example based on glass fibers,have good penetrability by highly viscous liquids and binding powders,they are not capable of absorbing and retaining such binder substancesin a binding manner in large amounts within the meaning of a depotformation.

SUMMARY OF THE INVENTION

The object of the present invention is to define a fiber-based carrierstructure having the features mentioned at the outset, produced, forexample, from loose fiber fillings of randomly arranged/oriented finitefiber materials, which, when shaped in a mat-like manner orthree-dimensionally as a reinforcing fiber pre-product, exhibits a highand controllable impregnability with viscous liquids and powders and atthe same time is able to retain large amounts of these substances in theinside in a uniformly distributed manner.

This object is achieved by a fiber-based carrier structure of thegeneric type mentioned at the outset having the features of the mainclaim.

Other features which are considered as characteristic for the inventionare set forth in the appended claims.

Although the invention is described herein as embodied in a fiber-basedcarrier structure for liquids and solid particles and a method forproducing the fiber-based carrier structure, it is nevertheless, notintended to be limited to the details shown, since various modificationsand structural changes may be made therein without departing from thespirit of the invention and within the scope and range of equivalents ofthe claims.

The construction and method of operation of the invention, however,together with additional objects and advantages thereof will be bestunderstood from the following description of specific embodiments.

DETAILED DESCRIPTION OF THE INVENTION

The invention provides a fiber-based carrier structure for producingfiber-reinforced composite materials which, through the use of a definedmixture of finite randomly arranged fiber bundles and finite randomlyarranged single fibers, is particularly suitable for absorbing liquids,melts and/or solid particles. The impregnability and the absorptioncapacity for liquid, also viscous, and/or solid pulverulent substancescan be adjusted via the mixing ratio of fiber bundles:single fibers. Thefiber carrier structure has a uniform structure in terms of length,width and thickness and is distinguished by an open-cell pore systemthat is openly accessible from the outside.

The fiber carrier structure according to the invention does not consistof at least two different product zones of different compositions andorientations, as described in international patent disclosure WO2012/072405 A1, or of a core and a cover layer of continuous fibershaving a completely different structure, as described in internationalpatent disclosure WO 2010/139077.

The finite fiber bundles in the present invention preferably result fromreinforcing fiber bundle pieces or multifilament yarn pieces which wereoriginally continuous but have been reduced to finite lengths, in whichthe single fibers adhere to one another in parallel in a mechanicallydetachable manner over at least 50% of the length thereof by non-naturalbinding means. They can, however, also be fiber materials from recyclingprocesses, if these are obtained in the form of bundles within themeaning of this invention.

With this definition, the known fiber bundles of natural fibers such asflax, hemp, untreated cotton and kenaf are excluded.

These long fibers in the fiber bundle which adhere to one another inparallel and in a mechanically detachable manner are substantiallydifferent from the fiber bundles mentioned in the literature, forexample in the case of the intermeshing or needling of nonwovens, whichare formed from single, isolated fibers over only a short length <<50%of the fiber lengths, for example when random fibers are broughttogether in an intermeshing hook or in the barbed hook in the case ofneedling. In contrast to the finite fiber bundles described in thepresent application, the fiber bundles described in the literature areheld together only locally by external pressing forces or bindingpoints. They form only during textile processing and are also referredto in the specialist literature as mechanical consolidation points,whereas the fiber bundles in the described invention are already presentin the starting material, the fiber material, and are not formedpurposively during the processing operation.

The single fibers used in the mixture that is employed can consist ofthe same or a different polymer as the fiber bundles that are used. Thisspecial carrier structure formed of the two fiber systems, fiber bundlesand single fibers, in defined uniform or different thickness and/or massper unit area is stabilized mechanically, thermally and/or chemicallyand fixed in such a way that at least 10 and not more than 90% of theresulting, consolidated fiber carrier consists of fiber bundles having aminimum number of 10 single fibers that adhere to one another inparallel, and an open-cell pore system that is openly accessible overthe entire structure is formed. The pore system contains a plurality ofinterconnected voids, which are interconnected by transport channels inorder to be able to transport powders and/or liquids applied from theoutside into the voids.

It is provided according to the invention to produce the product from adefined mixture of single finite fibers and finite fiber bundles, toshape it to a surface or three-dimensionally and then to fix it. Theproportion of fiber bundles used thereby determines to a significantdegree the impregnability or the depth of penetration of highly viscousand pulverulent substances into the product layer. The proportion ofsingle fibers thereby determines to a significant degree thepenetrability of storable liquids or powders. The higher the proportionof fiber bundles in the structure, the higher the proportion of largervoids with macropores and partially continuous channels; the higher theproportion of single fibers in the structure, the higher the proportionof smaller voids. The voids are thereby interconnected by transportchannels in order to be able to transport powders and/or liquids ormelts applied from the outside into the voids. Surprisingly, it has beenshown that the impregnability of such a structure with viscous liquidsand powders changes in accordance with the proportions by mass of singlefibers to fiber bundles. The higher the proportion of single fibers, thelonger impregnation takes and the poorer the penetration of a powderinto the structure.

It is provided according to the invention that this effect ispurposively developed and controlled via a purposively adjustablemixture of the two components. Therefore, in the case of the productaccording to the invention, defined proportions of finite fibermaterials of the same or different types are processed in two forms, abundle-like, non-unraveled form and a single-fiber form, in such amanner that, in a nonwoven-like mat or a three-dimensional molding, atleast 10% but not more than 90% of the fibers used still remain in theform of non-unraveled bundles, and the further usability as a fiberpre-product for reinforcing plastics materials is thereby significantlydetermined. In a preferred embodiment, the fiber bundles and the singlefibers are in a random arrangement without a defined orientation, as isachieved, for example, by a random loose filling material.

Such mixtures can be produced in a defined manner on the one hand bygravimetric weighing of one or more fiber components in bundle form withone or more single-fiber fiber components and subsequent mixing, forexample by a textile mixing technique. On the other hand it is possible,starting from a starting material that is >90% in fiber-bundle form, toproduce a ratio by mass between fiber bundles and single fibers that isadjustable according to opening intensity by subsequent processingoperations such as textile fiber opening by openers, treatment by meansof a mill (see published, non-prosecuted German patent applicationDE102009023641) with a teaser, picker or units that operate in a similarmanner. The opening technique, number of passes and parameters to beused in conjunction with the nature of the starting material infiber-bundle form are to be adapted to one another in test series insuch a way that the desired residual proportion of bundles in theproduct is obtained. The main influencing parameters in the startingmaterial are the fiber bundle length and the intensity with which thesingle fibers adhere in the fiber bundles that are provided. Themechanically detachable parallel adhesion of the single fibers over alength >50% of the single fiber length in the bundles is significantlydetermined by the nature and amount of substances having an adhesiveaction that are foreign to fiber polymers and are found on the fibersurface, such as sizes and finishes. Uncross-linked and/or uncuredpolymers can also be used as binders in the bundles. The importantcriterion is that it must be relatively easy to separate the bundlesmechanically.

In this manner, it is technically possible to produce constantproportions of from 10% to 90% fiber bundles and the remainder as singlefibers in a fiber mixture which can subsequently be built up into aconstant or varying fiber layer of defined thickness and mass per unitarea by mechanical and/or pneumatic processing operations. The fiberbundles are characterized in such a way that they consist of at least 10mutually adhering parallel single fibers which adhere to one anotherover at least 50% of the length thereof. The fiber bundles can bemechanically separated into smaller bundles or single fibers relativelyeasily and without damaging the fibers.

This mixture of fiber bundles and single fibers having a definedproportion of fiber bundles and single fibers that remains constant overthe production time leads to a defined thickness and mass per unit areaprofile, it being possible for both the thickness and the mass per unitarea to be developed uniformly or purposively differently over time andarea during the formation of the loose fiber filling.

Conventional fiber-processing units of the textiles field, such asopeners, mixing chambers, filling hoppers, airlay and fiber-blowingsystems, can be used for the production and processing of this fibermixture of bundle-like and single-fiber components, but such units mustbe modified technically and technologically in such a way that thedesired mixing ratio of bundle-like components and individual fibers isensured. Such modifications include reducing the number of fiber-openingpasses, dispensing with carding and roller carding in the processingoperation, reducing opening roller speeds, using coarser rollercoverings during mixing, homogenization and metering, and increasing thedistances between operating units having an unraveling action. Incontrast to the prior art, all the measures have the purpose of notunraveling or only unraveling to a lesser degree the fiber bundlecomponents that have an advantageous effect in the end product.Therefore, in a preferred embodiment, carding and roller carding is notused in the processing operation. The nature of the modifications isdependent on the system technology employed, the fiber material used,and the desired proportion of fiber bundles in the end product. All theinfluencing factors are therefore to be matched to one another in tests,and the necessary system and technology modifications are to be made.

Suitable units for laying the loose fiber layer of bundle-like andunraveled components are in principle mechanically and/or pneumaticallyoperating units, such as filling hoppers, airlay or fiber-blowingsystems. Here too, systems and methods must in particular be configured,via the above-mentioned measures, in such a way that, on the one hand,they act to homogenize the mixture and, on the other hand, thefiber-opening effect brought about by their fiber-opening/unravelingintensity is defined and only such that the desired target range offiber bundle proportion and single fiber proportion is reached. Iffiber-opening units are used to a certain degree, the unraveling actionof those units must be taken into account through a higher proportion offiber bundles in the starting material that is provided. This mixture offiber bundles and single fibers is laid randomly.

During the operations of mixing and homogenizing and of laying the fiberlayer, pulverulent substances, thermally binding components or liquidbinders that are not originally a constituent of the fibers and/or fiberbundles used can be introduced at the same time. These bindingcomponents are used to fix the pore system and the carrier structure ofsingle fibers and fiber bundles and/or as a binding component in theformation of the fiber-reinforced composite materials. After the loosefiber layer of homogeneously distributed fiber bundles and single fibersin defined proportions has been formed, it is necessary to fix thisspecial structure and render it pressure and traction-stable to handlingstresses. For this purpose, it is possible to use mechanical methodssuch as needling or intermeshing or binder consolidations of looselayers containing binders or thermoplastics.

The action of contact or radiation heat or the passage of hot air has amelting action or dry liquid binder components. The application ofbinders for fixing the pore system and the carrier structure of singlefibers and fiber bundles and/or as a binding component in the formationof the fiber-reinforced composite materials after the formation of theloose layer in the form of powder application or spraying is likewisetechnically possible and is determined by the intended use of theconsolidated layer. Here too, consolidation is generally carried out bya heat treatment that dries the binder or that effects melting or thestart of melting. By these processes, the pore system purposivelyproduced in the nonwoven pre-product is fixed. The open pore system ofthe nonwoven-like pre-product consists of small voids, which form inparticular as gaps between the random, intersecting single fibers ofvery small diameter, and larger voids, which form as gaps between therandom intersecting fiber bundles of substantially larger diameter.Depending on the proportion of fiber bundles in the single fibers, acorrespondingly finer or coarser open-pore void system or pore systemwith differing impregnability and substance storage capacity is formed.In the subsequent further processing, these pores or voids, which arepurposively adjustable according to the proportions of single fibers andfiber bundles, perform the function of binder transport, or binderinfiltration of the nonwoven pre-product and of fixing the binder in thenonwoven pre-product. The coarser, open pore system forms transportchannels for thick, viscous binding resins and powders, which channelsextend into the center of the nonwoven layer. It is thus possible tosubstantially assist with a desired complete, continuous impregnationwith viscous liquids and powders, which simplifies impregnationtechnology in terms of costs and technology, shortens impregnation timesand makes it possible to use thicker reinforcing fiber pre-products. Thefiner pores based on the single fibers in the product ensure that thebinder components that have penetrated are retained and incorporated inthe product in the manner of a sponge.

The proportion of fine and coarse pores is determined by the respectiveproportions of coarse fiber bundles and fine single fibers in thenonwoven. Depending on the thickness of the nonwoven, the impregnatingmedium to be used to form the consolidated carrier structure or thefiber-reinforced molding and the infiltration technology, theproportions of fiber bundles and single fibers are to be tested andspecified in preliminary tests for the fiber material to be used in eachparticular case. By mechanical needling or a similar process, verticalpuncture channels can be formed in addition to the existing porestructure, which channels assist with the transport of binder into thenonwoven layer and influence the function of the impregnability. Bycompressing the loose fiber layer, the penetrability of the nonwoven isgenerally reduced and the depot action is reduced. In the interplay ofpressing processes for reducing the thickness of the nonwoven andrelated nonwoven consolidation, the impregnability that is produced isagain purposively influenced and fixed in terms of the final quality andquantity thereof.

The use of these fiber pre-products having defined fiber-bundle-likeproportions is concentrated in the field of fiber composite materials.Accordingly, the fiber materials used reside in the field ofconventional reinforcing fiber materials. They can be organic fibermaterials such as para-aramids as well as glass and carbon fibermaterials including fiber materials of this type from various recyclingprocesses.

Examples Practical Example 1

Starting from a starting material based on mechanically prepared carbonfiber non-crimped fabrics having a high proportion of fiber bundles,loose fiber fillings having different proportions of fiber bundles wereproduced by different fiber opening intensities on a roller opener(material 1) and a carding machine 2 (material 2) and were built up to auniform mass per unit area of 500 g/m² with a constant loose thickness.The carbon fibers used, which were from a mechanical recycling process,had a mean length of the fiber bundles of 45 mm.

For both fiber materials, the proportion of fiber bundles, based onmass, was determined by manual screening, the air through-flowresistance was determined by an air through-flow method as a measure ofthe open-pore nature and accessibility to particles and liquids, and thedrop sink-in time was determined by means of a drop test using a morehighly viscous liquid in accordance with the TEGE-WA drop test as ameasure of the impregnability.

The following results were obtained:

Parameter Unit Material 1 Material 2 Proportion of fiber bundles* [%]80.5 51.9 Air through-flow resistance as a [mm 377 430 measure ofporosity** isopropanol] Sink-in time in the drop test*** [s] 120-150280-310

The proportion of fiber bundles was determined by manual screening of afiber sample of 1 g, weighing the bundle components from at least 10single fibers and calculating the proportion by mass in percent.

** The air through-flow resistance was determined on the basis of apublication from 1964 by Geitel, K.: “Zur Theorie der Luftströmung durchFaserpropfen” [The Theory of the Flow of Air Through Fiber Pads], in“Faserforschung and Textiltechnik” [Fiber Research and TextileEngineering] 15 (1964) Volume 1, p. 21-29. The theory of the flow of airthrough fiber pads is described here. According to that publication, thepressure drop over an amount of fibers through which a medium flows isdependent on

the amount of air that flows per unit time,the dimensions of the measuring chamber (diameter, height),the viscosity of the flowing medium,the porosity of the fibers, andthe fiber surface area.

By means of a type 4/15/1 wool fineness tester from Medimpex (Hungary),the porosity of a fiber pad was determined by this air through-flowmethod. The fiber pad is in this case the test specimen, formed from thecarrier structure produced according to the example. All the parametersapart from the fiber material to be tested were kept constant. The airresistance generated by the fiber pad is read off from the measuringinstrument in [mm] of an isopropanol liquid column. The column height in[mm] is directly proportional to the air through-flow resistance that isestablished and thus indirectly proportional to the porosity. The testswere in each case carried out on 1.4 g of fiber material at an airthrough-flow speed of 400 l/min.

In the modified drop test, a CMC solution having a viscosity (25° ° C.)at a shear gradient of 2/s of 1.7 Pas was used as the test liquid. Themass of the test drop was 0.5 g in all cases.

Practical Example 2

Starting from a starting material based on mechanically prepared carbonfiber non-crimped fabrics and having a high proportion of fiber bundles,the starting material was intimately mixed with 7% of a thermallysoftening binding fiber GRILON MS 6.7 dtex/Varioschnitt via a mixing bedand 1 mixing pass by means of a coarse opener using a mixing/opening pinroller and supply of the material via a roller pair. Half of thisconstant starting fiber mixture of recycled carbon fibers having a highproportion of fiber bundles and thermally softening binding fibers in amixing ratio of 93/7 was then laid via an FBK 536 feeder from Tru{umlautover (t)}zschler at 2 m/min to form a loose filling of 370 g/m². Theother half of the starting material was processed as comparativematerial by carding twice with a roller card using three worker/stripperpairs at 10 m/min to form card web and placed in loose layers one abovethe other by means of crossplaiters so that a mass per unit area of 370g/m² was obtained.

The two loose fiber layers, feeder layer and carded and laid layer, werethen partially consolidated to a mat by means of a Thermofix from Schott& Meissner at a throughput speed of 2 m/min, a heating temperature of190° C. and with a gap of 1.5 mm, in which the two fiber layers areguided in succession through the thermal consolidation system between anupper and a lower transport belt, and the void and pore structuresformed were fixed.

The water absorption according to DIN 53923 was then carried out on bothnonwoven mats as a measure of the storage capacity for liquids. Beforethermal consolidation, the proportion by mass of fiber bundles in thetwo loose fiber layers was determined.

The following results were obtained:

Type of nonwoven mat Sample Laid by feeder Laid by carding machine Waterabsorption according to DIN 53923 1 1202% 929%  2 1069% 930%  3 1097%866%  4 1065% 846%  5 1097% 902%  Mean 1106% 895%  Proportion of  85%6.6% fiber bundles

Whereas a high proportion of fiber bundles was used in the firstfiber-based carrier structure according to the invention (ratioproportion of fiber bundles to single fibers approximately 5.66:1), theproportion of single fibers is comparatively high in the case of thenonwoven mat laid by carding machine that was used as comparativematerial (on the right in the above table) (ratio proportion of singlefibers to fiber bundles approximately 14.15:1). The above table showsthat the water absorption is substantially higher in the case of thecarrier material according to the invention than in the case of thecomparative material.

1. A fiber-based carrier structure for liquids, melts and solidparticles, comprising: industrially produced reinforcing fiber materialshaving finite single fibers in a random configuration as a firstreinforcing fiber component and finite fiber bundles as a secondreinforcing fiber component, said finite single fibers and said finitefiber bundles being present as a mixture in a defined mixing ratio offrom 1:9 to 9:1, said finite fiber bundles having a fiber lengthdistribution; and a pore system being open-cell and openly accessiblefrom an outside.
 2. The fiber-based carrier structure according to claim1, wherein said finite single fibers and said finite fiber bundles arepresent in an isotropic, random configuration.
 3. The fiber-basedcarrier structure according to claim 1, wherein said pore system is apore structure having a loose fiber filling being partially consolidatedand mechanically, thermally and/or chemically stabilized and fixed. 4.The fiber-based carrier structure according to claim 1, wherein singlefibers in a mixture of said finite fiber bundles and said finite singlefibers have been obtained by incomplete opening of fiber bundles.
 5. Thefiber-based carrier structure according to claim 1, wherein said finitefiber bundles have a bundle thickness of at least 10 single fibers whichadhere to one another in parallel over at least 50% of a fiber length.6. The fiber-based carrier structure according to claim 1, wherein atleast a proportion of said finite single fibers have a fiber lengthdistribution.
 7. The fiber-based carrier structure according to claim 1,wherein said finite fiber bundles have a mean length which is differentfrom that of said finite single fibers.
 8. The fiber-based carrierstructure according to claim 1, further comprising at least one ofsoftenable binding fibers or a powder which are added, in a uniformlydistributed manner, before a fiber layer is formed.
 9. The fiber-basedcarrier structure according to claim 1, wherein the industriallyproduced reinforcing fiber materials used as a starting material have auniform substance nature and geometry or are a mixture of fibermaterials of different substances and/or geometry.
 10. A method forproducing a fiber-based carrier structure, which comprises the steps of:weighing gravimetrically at least one fiber component in bundle form andat least one single-fiber fiber component; and mixing the least onefiber component in bundle form and the at least one single-fiber fibercomponent using a textile mixing technique resulting in a fiber mixture.11. The method for producing a fiber-based carrier structure accordingto claim 10, which further comprises laying at least one ofvolumetrically or pneumatically, the fiber mixture, in a layer having athickness of from 0.5 to 20 cm loosely and without prior orientation.12. The method for producing a fiber-based carrier structure accordingto claim 10, which further comprises laying at least one ofvolumetrically or pneumatically, the fiber mixture, in a layer having athickness of from 2 to 10 cm, loosely and without prior orientation.